The manufacture of reinforcing glass yarns is carried out, in a known way, starting from streams of molten glass flowing out of the orifices of bushings. These streams are drawn in the form of continuous filaments, and these filaments are then brought together into base yarns, which are then collected.
Before they are brought together into the form of yarns, the filaments are coated with a size by passing over a sizer. This deposition is necessary for obtaining the yarns and allows them to be combined with other organic and/or inorganic materials in order to produce composites.
The size firstly acts as a lubricant and protects the yarns from the abrasion that results from high-speed friction between the yarns and various devices during the aforementioned process.
The size may also, especially after it has cured, provide the aforementioned yarns with integrity, i.e. the mutual bonding of the filaments within the yarns. This integrity is especially desired in textile applications in which the yarns are subjected to high mechanical stresses. This is because, if the filaments are poorly held together, they break more easily and disrupt the operation of the textile machinery. What is more, nonintegrated yarns are considered to be difficult to handle.
However, the size is also employed in cases in which this integrity is not desired, such as in the case of reinforcing fibers, when a high rate of impregnation with the material to be reinforced is desired. Thus, in the manufacture, for example, of pipes using direct impregnation and filament winding techniques, open yarns in which the filaments are separated from one another are used. Small quantities of size, especially less than 0.5% by weight, are then used.
The size also facilitates the wetting and/or impregnation of the yarns by the materials to be reinforced and helps to create bonds between said yarns and said materials. The mechanical properties of the composites obtained from the material and from the yarns depend in particular on the quality of the adhesion of the material to said yarns and on the ability of said yarns to be wetted and/or impregnated by said material.
Most sizes currently used are aqueous sizes which are simple to handle but which must be deposited in large quantities on the filaments in order for them to be effective. Water generally represents more than 90% by weight of these sizes (especially for viscosity reasons), and this means that the yarns have to be dried before they are used, it being possible for water to impair the good adhesion between the yarns and the materials to be reinforced. These drying operations are lengthy and expensive and their effectiveness is not always optimal; they require the use of large-capacity ovens. In addition, when they are carried out during the fiber-forming operation (that is to say before the yarns obtained by converging the filaments have been collected), either on filaments (WO 92/05122) or on yarns (U.S. Pat. No. 3,853,605), they require the installation of dryers under each bushing and, when they are carried out on yarn packages, they run the risk of causing irregular and/or selective migration of the components of the size within the packages (aqueous sizes already have a tendency to be distributed over the yarns in an irregular manner because of their nature) and possibly of causing yarn-coloration or package-distortion phenomena. Moreover, without drying, package distortion is often observed on straight-sided packages (rovings) of fine yarns (i.e. yarns having a “count” or “linear density” of 300-600 tex (g/km) or less) which are coated with aqueous sizes.
It is to remedy these drawbacks that a novel type of size, which is virtually free of solvents and called an anhydrous size, has been developed. Anhydrous sizes are curable and/or crosslinkable solutions which optionally contain organic solvents and/or water in small amounts, generally of less than 5% by weight. They are distinguished advantageously from aqueous sizes by their ability to be distributed in a homogeneous and uniform manner on the surface of the filaments, i.e. forming films of constant thickness, and by the fact that they make any subsequent drying or solvent-removal treatment unnecessary since the small quantities of solvent evaporate during deposition of the size on the filaments and during curing of the size.
Furthermore, the quantities of anhydrous size deposited on the filaments are 30′ much less than those of aqueous size; thus, when depositing by means of a sizing roller, a film is formed on the surface of the latter with a thickness not exceeding 15 μm in the case of an anhydrous size instead of a film with a thickness of approximately 90 μm in the case of an aqueous size. Moreover, these small quantities of anhydrous size are deposited on the filaments with a much higher efficiency, possibly reaching 100% when the operating conditions are chosen judiciously, whereas this efficiency is generally about 40 to 75% with aqueous sizes.
Anhydrous sizes fall mainly into three categories.
The first category encompasses UV-curable sizes as described in patent EP 0 570 283 and comprising, for example:                at least one mono-unsaturated or polyunsaturated monomer and/or oligomer of the polyester acrylate, epoxy acrylate, silicone compound or urethane acrylate type;        at least one photoinitiator, such as benzoin, acetophenone, benzophenone, sulphonylacetophenone and their derivatives, as well as thioxanthones;        if necessary, at least one organic solvent; and, optionally,        additives such as at least a wetting agent, an adhesion promoter, an antishrinkage agent, a compatibilizer consisting especially of a silane.        
The second family of anhydrous sizes is that of thermally curable and/or crosslinkable sizes, as described in patent applications FR 2 713 625 and 2 743 361.
By way of example, the basic system of these compositions comprises:                an acrylic component and a heat-activated radical-initiating peroxide; or        an epoxy component and an anhydrous constituent which cure by reacting with each other.        
The third category of anhydrous sizes forms part of the teaching of applicant FR 97/05926: these are room-temperature curable sizes, the basic systems of which may contain one or more homopolymerizable monomers and/or at least two copolymerizable monomers which require no external supply of energy. In the case of copolymerization of two monomers, these may be deposited on the filaments in the form of their mixture in solution, immediately after this mixture has been formed, or in the form of a first stable solution containing a first monomer mixture and of a second stable solution containing a second monomer mixture. In the latter variant, the first solution is applied to the filaments and the second is applied subsequently thereto, at the latest while the filaments are being combined into yarns. Be that as it may, the copolymerization generally starts on the filaments as soon as the first and second monomers come into contact with each other and, if necessary, with the required catalyst or catalysts.
The UV-radiation treatments and heat treatments required to cure the sizes of the two first types mentioned above are carried out in one step or in several steps, after the filaments have been brought together into yarns. Thus, depending on the envisaged use and on the nature of the yarns, an irradiation or heat pretreatment is sometimes carried out at the time of collecting the yarns in various forms of packages, in order to precure the size, the actual curing of which is carried out in a subsequent radiation or heat treatment when the yarn is unwound for the specific application for which it is intended, namely a textile application or an application of reinforcing organic or inorganic materials. This is because the yarn coated with the as yet uncured composition does not exhibit integrity in the ordinary sense of the term since the sheathed filaments of which the yarn is composed may slip over each other. This yarn can therefore be handled easily and, when it is wound in the form of packages, can be easily extracted from the packages without first having to undergo a treatment to cure the size. The yarn coated with the as yet uncured size composition has, moreover, a very high capability of being wetted and impregnated by materials to be reinforced, it thus being possible for impregnation to take place more rapidly (increase in productivity) and the composites obtained thus having a more homogeneous appearance and having certain of their mechanical properties improved.
However, as described in patent EP-0 570 283, curing the size by the UV irradiation of a yarn in the form of a package may also have advantages.
With regard to depositing anhydrous sizes on glass filaments, several techniques are known. Thus, according to application FR 2 763 328 already mentioned, this deposition is carried out with the aid of a roller or of a sprayer, with the aid of a device which also acts as a converging means, or by the use of other yarns or filaments coated with the composition and brought into contact with the glass filaments. The latter technique makes reference to the special case of producing composite yarns, consisting of comingled glass filaments and thermoplastic polymer filaments or yarns.
By definition, deposition by spraying is inevitably accompanied by quite a significant amount of loss of size; the recovery of this lost proportion, assuming that it is possible, constitutes a handicap.
The method of deposition by means of a roller or of a device for converging the filaments into yarns consists of taking up size from a somewhat viscous and thick liquid film formed on a smooth surface, having ranges of physical properties, especially surface hardness and surface microporosity, of the type of those of metal surfaces. Starting from the observation that the chemical nature of the anhydrous sizes allows them to be used in ever lower quantities, there is currently a requirement for a process for forming an ever thinner liquid film, of perfectly uniform, controllable and reproducible thickness, on a macroscopically smooth surface of the metallic, ceramic or organic type. This is because it may be expected that the take-up of size onto the filaments from such a film results in the filaments being coated with a minimum quantity of size, with an increased deposition efficiency, i.e. a reduction in the amount of size lost, and for this to be achieved under completely controlled conditions. Finally, the aim is, of course, to obtain filaments and yarns, and reinforced materials containing them, which have sufficient, or at least preserved, mechanical properties or even in certain respects novel mechanical properties.
Currently, there is no process making it possible to form, in a controllable manner, a thin film of anhydrous size at the surface, for example, of a metal roller. This is because the immersion of the lower part of the roller in the size solution coupled with the rotation of the roller results in the formation, at the surface of the roller, of a layer whose characteristics can be controlled only to a small extent by varying the viscosity of the solution and the rate of rotation of the roller. The thickness of this layer is too great and irregular, and it is impossible to avoid loss of size, in the device for bringing the filaments together into yarns or for collecting the yarns, by the size being thrown off under the effect of the inherent centrifugal force at the high winding rates employed.
Moreover, no system for depositing size on a sizing roller with the aid of a metering pump and of an injection nozzle has yet allowed the formation of the desired film.
Furthermore, the previously-mentioned patent EP 0 570 283 briefly mentions, in its part describing FIG. 1, a coating device 13 consisting of an applicator provided with a felt moistened with a reactive mixture using a metering pump. This is because the structure of a felt allows it to soak up a solution in a particularly homogeneous manner. However, the take-up of size suggested by the European patent, from the felt onto the glass filaments, is not satisfactory in the context of the technical problem mentioned above since the deposition of the required small quantities of size on the filaments could not be achieved except at the cost of the felt drying out somewhat, a situation which, given the naturally irregular structure of the felt, the surface of which has fibers of varied dimensions, directions or even textures, would run the risk of the glass filaments catching thereon and therefore the risk of said filaments breaking. Only relatively large amounts of size can thus be deposited in the manner described in the document.
According to an advantageous approach, application FR 2 767 539 proposes, in a process for manufacturing a continuous yarn, which consists in forming a multiplicity of continuous filaments by the mechanical drawing of a multiplicity of streams of molten thermoplastic(s) (particularly molten glass), in depositing a mixture, in the liquid state, in particular an anhydrous size, on the surface of the filaments before they are brought together into at least one yarn, according to the following technique. A mat of mechanically held-together fibers, of the felt or woven fabric type, is continuously impregnated with the liquid mixture, at least some of which is continuously taken up by means of a rotating roller in contact with the mat; it is by using this sizing roller that the mixture is deposited on the filaments while they are being drawn. The material of the sizing roller is of course selected so as to withstand the abrasion due to the rubbing of the filaments. This technique makes it possible to deposit on the surface of the filaments quantities of size as low as 0.5 to 1% by weight with respect to the weight of the filaments, which quantities are sufficient in the case especially of currently known high-performance anhydrous sizes, with a deposition efficiency close to or equal to 100%. A liquid film of anhydrous size with a constant thickness of less than 8 μm may be formed on the surface of the sizing roller in a perfectly reproducible and controllable manner. Since the loss of size is reduced practically to nothing, a sizing rate as low as 160 to 350 g/h will be sufficient for a bushing producing 800 kg of filaments per day.
Moreover, the French patent application discloses that the mat is positioned in an inclined plane and is fed with size drop by drop flowing onto the upper part of the mat, so that the size diffuses over the entire surface of the mat both under gravity and by a capillary effect. Furthermore, it should be pointed out that in the industrial implementation of this technique the dimensions of the sizing roller and of the mat are necessarily greater than the surface area of all of the filaments to be sized, as the latter are frequently subjected to lateral displacements, and it is necessary, of course, to ensure that all of the filaments are at any moment in contact with the sizing roller, which itself has to be provided with a uniform film of size over the entire part of its surface in contact with the filaments. However, it is not possible to prevent the lateral end regions of the sizing roller from hardly or even never coming into contact with filaments, since these regions are largely dimensioned in order to guarantee that the mixture is deposited on all the filaments. One of the consequences of this is the presence of a relatively stagnant mixture, both in these lateral end regions of the sizing roller and in the corresponding regions of the mat. It has also been observed that in these regions the liquid mixture may, depending on the type of size, undergo a reaction owing to the action of external elements such as water, carbon dioxide and high temperature, forming condensates or gels, this type of chemical reaction moreover having a tendency to propagate toward the center of the mat and of the sizing roller, including in the regions of the latter which actually participate in transferring the mixture onto the filaments. This phenomenon causes drying regions on the surface of the roller. This insufficient presence of size results in imperfect protection of the filaments, which is manifested by the formation of fuzz or the breakage of filaments in the sheet.